What is the underlying cause of Eliza's anger with Higgins in act 4?

Professor Higgins and Colonel Pickering spend the evening after the party in self-congratulatory celebration, ignoring Eliza and her contribution to the success of the deception. Eliza, understandably is infuriated by Higgins' conceit, but the final straw was his condescending dismissal, telling her to "go to bed like a good girl and sleep it off."

Eliza understands that her entire life (and livelihood) is forever altered by her transformation, but Higgins appears both unobservant and unconcerned. His telling Eliza to just marry well is an insult to Eliza's integrity, and she lets him know that as a scientist he may have succeeded, but as a human he failed miserably.